China also reportedly has told Chinese media that they must report only news of missing Malaysia Airlines Flight MH370 that has been issued by the government’s Civil Aviation Administration and the state-run Xinhua news agency.

By Stuart Leavenworth - McClatchy Foreign Staff

China has dispatched a delegation to Malaysia amid mounting frustration here on how authorities there are handling the investigation of a missing airliner that had 239 people aboard, including 153 Chinese citizens.

China’s Foreign Ministry said the delegation was scheduled to arrive in Kuala Lumpur, Malaysia’s capital, late Monday and begin work immediately on the fate of MH370, which has been missing and presumed crashed since early Saturday.

The group “will urge the Malaysian side to intensify search and rescue efforts, to find out the fact of the incident as soon as possible, to timely release the accurate information and to well serve the family members of the passengers to Malaysia at the same time,” the Foreign Ministry said in a statement.

Friends and relatives of Chinese passengers on the flight have lashed out at Malaysian officials for failing to keep them informed and helping some of them obtain passports and visas so they can fly to Kuala Lumpur.

More than 100 of them have signed a petition seeking information and assistance about the flight, which left Kuala Lumpur early Saturday morning in route to Beijing.

At a Beijing hotel on Monday, some relatives and friends threw water bottles at Malaysia Airlines officials in a melee that was captured on video.

The mystery surrounding MH370 is hardly the first time an airliner presumed crashed could not be found for a lengthy period of time. Yet the dribs and drabs of often contradictory information from investigators have been particularly anguishing for people trying to find out what happened to their loved ones.

On Monday, it was reported that a Vietnamese search crew had spotted what appeared to be the door of the plane in the waters separating Vietnam and Malaysian. That was later reported to be false. Officials also said that an oil slick in the area was not composed of fuel from the Boeing 777 aircraft.

As of Monday, some 34 aircraft and 40 ships from Vietnam, Malaysia, Thailand, Australia, Singapore, Indonesia, China and the United States had been deployed to search for the plane.

Yet numerous analysts say the search is not being well coordinated from Kuala Lumpur, which has asked the United States and other countries for assistance. Two investigators from the United States’ National Transportation Safety Board and two officials from the Federal Aviation Administration arrived Monday in Kuala Lumpur, U.S. State Department spokeswoman Jen Psaki said.

Questions abound on how at least two men were able to board the flight with stolen passports, a security breech that may or may not have had anything to do with the plane’s disappearance.

At a briefing Monday in Kuala Lumpur, Malaysia’s civil aviation chief, Azaharuddin Abdul Rahman, said officials had examined surveillance tapes of the plane’s boarding “from check-in right to departure.”

He later said that the two men who used the stolen passports were “not Asian-looking males.” Upon further questioning, he said that one man appeared to be black.

While the stolen passports have raised concerns that the flight might have been brought down by terrorists, security experts note that stolen passports are readily available in Southeast Asia and are often used by drug smugglers and illegal immigrants.

Even so, Malaysian authorities are sending fingerprints and photos of two men who boarded the flight to U.S. authorities. The two men reportedly had tickets to fly to Amsterdam through Beijing, meaning that they didn’t have to undergo the kind of background checks required for a Chinese visa.

Although China is attempting to portray itself as being aggressive in pushing the investigation forward, it is also trying to control the flow of information that is reaching the public here.

According to China Digital Times, a Berkeley-based site that monitors Chinese media, the government sent a directive to Chinese reporters requiring them to report only news about MH370 issued by the government’s Civil Aviation Administration and state-run Xinhua news agency.

“All media must refrain from interviewing family members without permission, and must not incite any discontented sentiment,” said the directive. It also urged Chinese journalists to increase publicity of the ongoing “Two Sessions” meeting of China’s rubber-stamp parliament, which has been overshadowed by the air disaster.